(1) Field of the Invention
The present invention relates to a novel ionomer composition. More particularly, the present invention relates to an ionomer composition having an excellent antistatic property and an excellent heat moldability. Furthermore, the present invention relates to uses of this ionomer composition as an antistatic agent and an antistatic resin composition.
(2) Description of the Prior Art
In general, molded articles of thermoplastic polymers are readily charged with static electricity, and it is well-known that various troubles are caused by charging with static electricity while these molded articles are used or processed. Various methods have been proposed and practised as the antistatic method for these molded articles. However, these methods are defective in some points or other. For example, the method comprising kneading an antistatic agent into a resin composition, which is generally adopted, is defective in that the surface is made sticky or stained by bleeding of the antistatic agent, the change of the electroconductivity by external conditions is large and the attained antistatic effect is not durable. Moreover, the method comprising adding an electroconductive filler such as electroconductive carbon is defective in that no stable antistatic effect can be attained unless the electroconductive filler is added in a large amount, the obtained molded article therefore becomes opaque, and the filler falls from the surface of the molded article to cause contamination. Furthermore, there is known a method in which the surface of a molded article is covered with an electroconductive material such as a metal or a metal oxide by coating or vacuum deposition. However, this method is defective in that the method can be applied only to a molded article having a simple shape, the manufacturing cost increases and the molded article becomes opaque.
As the means for obviating these defects, there has already been proposed a method in which an antistatic property is given to a polymer per se. For examples, Japanese Unexamined Patent Application No. 60-240704 discloses an electroconductive resin comprising an ionomer formed by neutralizing an ethylene/unsaturated carboxylic acid copolymer with an alkali metal selected from the group consisting of Na, K, Rb and Cs, wherein the amount of the alkali metal is at least 1.3 millimoles per gram of the resin. When we examined this proposal, it was found that although the above-mentioned defects of the conventional techniques can be overcome by this proposal, the proposal involves the following problems. Namely, in order to obtain a sufficient antistatic effect, it is necessary that the alkali metal should be contained in an amount of at least 1.5 millimoles per gram of the resin, and therefore, the moisture-absorbing property of the ionomer increases and a trouble of foaming is often caused at the molding step. Furthermore, since the alkali metal is contained at a high concentration, it is inevitably necessary that the content of the unsaturated carboxylic acid in the ethylene/unsaturated carboxylic acid copolymer should be increased, and this increase of the content of the unsaturated carboxylic acid results in lowering of the melting point of the ionomer and degradation of the heat resistance and the application field is limited. Moreover, the manufacturing cost of such a copolymer having a high unsaturated carboxylic acid content is large.